When the slow-mo thing stops and you begin to play, go behind the red circus cart, then use cover. While Piggy is looking for you shoot him right in the head. Then, while he is stunned, run to the bottom of that little hill where the big gun is, use that as cover and while hes stunned again shoot him in the head as many times an you can.
Note: DO NOT SHOOT HIM IN ANYTHING BUT THE HEAD AND STOMACH, if you do he will see where you are and blow you up!

Happy Playing!!